1. Field of the Invention.
The present invention relates to improved methods and compositions for consolidating unconsolidated subterranean zones, and more particularly, to improved low viscosity hardenable epoxy resin compositions and methods for consolidating unconsolidated subterranean producing zones.
2. Description of the Prior Art.
Oil and gas wells are often completed in unconsolidated producing zones containing loose and incompetent sands which migrate with oil, gas and/or water produced by the wells. The presence of sand in the produced fluids is disadvantageous and undesirable in that the sand particles abrade pumping and other producing equipment and reduce the fluid production capabilities of the producing zones. Unconsolidated subterranean zones include those which contain loose sands that are readily entrained by produced fluids and those wherein the sand particles making up the zone are bonded together with insufficient bond strength to withstand the forces produced by the production of fluids through the zones.
Heretofore, unconsolidated subterranean producing zones have been consolidated into hard permeable masses by injecting a hardenable resin composition into the zones followed by an afterflush solution to remove excess resin from the pore spaces of the zones. Often, to insure that sand is not produced as a result of the consolidated zones having insufficient strengths to maintain their integrity, costly gravel packs have been installed in the well bores penetrating the zones. The gravel packs function to filter out sand from the fluids being produced.
An alternate technique which has recently been developed and used involves consolidating an unconsolidated zone by injecting a hardenable resin composition in the portion of the zone surrounding the well bore followed by an afterflush solution whereby the portion of zone surrounding the well bore is consolidated into a hard permeable mass. Thereafter, at least one fracture is created in the zone extending from the well bore through the consolidated portion of the zone into an unconsolidated portion thereof. A hardenable resin composition coated proppant is deposited in the fracture and the resin composition is caused to harden whereby the proppant is consolidated into a hard permeable mass which filters out and prevents the migration of formation sands with fluids produced through the fracture into the well bore. However, since the presence of the filtered sand adds to the resistance to the flow of fluids through the fracture and through the consolidated portion of the zone surrounding the well bore, additional pressure drawdown takes place which can cause the consolidated portion of the zone and proppant in the fracture to breakdown and to be bypassed.
In wells containing long producing intervals in unconsolidated zones, permeability variations in the zones through which the well bores extend are often encountered. As a result, leakoff of the hardenable resin composition to the more permeable parts of the zones often leaves the lower permeability parts untreated. This, in turn, allows the continued migration of loose and incompetent sands with fluids produced from the zones.
Thus, there are needs for improved hardenable resin compositions and methods whereby the compositions have high strengths upon hardening and have other improved properties for consolidating unconsolidated subterranean producing zones without the necessity of also installing costly gravel packs or the like. Further, in long producing interval applications, such improved hardenable resin compositions should include subsequently removable particulate solid diverting agents for diverting the resin compositions from highly permeable portions of the intervals to the less permeable portions.